The present invention relates generally to determining the erythrocyte sedimentation rate (ESR) in a blood sample. The standard laboratory method heretofore used for measuring ESR is the sso-called Westergren method. A general review of that method is provided in "ICSH recommendations for measurement of erythrocyte sedimentation rate" published in Journal of Clinical Pathology 1993; 46: 198-203.
Essentially, the Westergren method provides for a sample of blood to be collected in a test tube (pipette) to form a 200 mm blood column in the presence of an anticoagulant. After mixing the specimen briefly, the test tube is loaded into a device or an instrument including sensors such as an optical sensor to record the location of the blood/air meniscus at an initial time. After a period of 60 or 120 minutes, the operator or the sensor then identifies and measures the location of the cell/plasma interface. The distance in millimetres from initial blood/air meniscus and the final cell/plasma interface gives the typical Westergren output value for the test which is expressed in units of mm/hr.
A basic disadvantage of the conventional Westergren method lies in the considerable length of the test tube (typically in excess of 200 mm) which makes it unsuitable for use in collecting blood directly. Consequently, blood for the test has to be taken either by using a syringe or a pre-evacuated tube and the blood thus collected must then be transferred to the Westergren test tube. In addition to being unpractical, such a procedure exposes the operator to the danger of contacting the blood during the transfer process.
Systems dispensing with such a drawback and carrying out ESR determination using tubes significantly shorter than the standard 200 mm Westergren pipette are already available.
Exemplary of such prior art is, for instance, the ESR measuring system sold under the trademark SEDISCAN by the assignee of the present application. A SEDISCAN instrument is adapted for use in connection with tubes (sold under the trademark SEDITAINER--both SEDISCAN and SEDITAINER being registered trademarks of Becton Dickinson and Company) essentially comprised of 5 ml draw tube of 120 mm length and 10.25 mm outer diameter containing liquid sodium citrate/citric acid at 4:1 ratio. Using the above tube, the SEDISCAN instrument provides an extrapolated Westergren value after 30 minutes which compares well to actual 60 and 120 minutes Westergren values. However, it is necessary to examine nearly the entire tube length (about 70-80 mm of the blood column height of 100 mm) in order to predict the ESR. The tube is held vertically.
Another system using "short" tubes is sold under the trade name VESMATIC by the Italian company Diesse Diagnostica Senese S.r.l. The tube for use in this latter system has a rectangular shape overall and a triangular shape of the tube bottom. Again, nearly the entire tube length must be scanned which leads to using an additional plastics outer sleeve to apply patient bar code or identification labels. The outer sleeve and the patient identification data must be removed from the tube before this is placed in the instrument for carrying out the test Consequently, there is an actual danger that, due to the high number of tubes tested concurrently in a laboratory, a diagnostic result may be incorrectly assigned to the wrong patient due to a mistake in association of the clinical result for a tube with the patient identification contained on the removed outer sleeve.
So, it is practically a mandatory requirement for any test tube for proper use in ESR measuring test to carry patient identification data which must not and cannot be removed at any time, while carrying out the test.
Also, there is a growing trend in the field of ESR determination to provide reading of the test final values in a significantly shorter time than the standard 60 minutes of the Westergren method. Finally, the quantity of blood required for the test (and consequently the quantity of blood to be taken from the patient) is to be made as small as possible.